1. Field of the Invention
The present invention relates to a package structure and a package substrate thereof. More particularly, the present invention relates to a package structure and a package substrate thereof, capable of using a solder mask to form a groove to prevent a molding compound from contaminating a pad area.
2. Description of Related Art
The appearance of semiconductor chips is an important milestone of the modern science and technology. Generally, the semiconductor chip must be protected by a package structure, so as to protect the semiconductor chip from being affected by moistures or from being crashed. Referring to FIG. 1, it is a schematic view of a conventional package structure 900. The package structure 900 includes a package substrate 910, a chip 920, and a molding compound 930. The chip 920 is carried on the package substrate 910. The package substrate 910 has at least one wire-bonding pad 911 and at least one solder-ball mounting pad 912. An active surface 920a of the chip 920 is electrically connected to the wire-bonding pad 911 via a bonding wire 940. The molding compound 930 covers the cover chip 920 and the bonding wire 940, so as to protect the chip 920 and the bonding wire 940 from being affected by moistures or being crashed. A solder ball 950 is disposed on the solder-ball mounting pad 912, for connecting to a printed circuit board (not shown in FIG. 1), such that the internal circuit of the chip 920 is electrically connected to the printed circuit board through the bonding wire 940, the wire-bonding pad 911, internal wires of the package substrate 910, the solder-ball mounting pad 912, and the solder ball 950.
As the electronics are continuously developed towards a trend of “light, thin, short, and small”, the volume of the package structure 900 also must be reduced to cater to such an era trend. Generally, a certain space is required to connect the bonding wire 940 from the active surface 920a of the chip 920 to the wire-bonding pad 911 of the package substrate 910. Furthermore, after the molding compound 930 covers the bonding wire 940 and the active surface 920a of the chip 920, the whole structure 900 occupies a certain volume. Accordingly, in the package structure 900 of FIG. 1, the wire-bonding pad 911 and the solder-ball mounting pad 912 are disposed on the same surface of the package substrate 910. The package substrate 910 exposes the active surface 920a of the chip 920 via an opening 910c. Therefore, when the molding compound 930 covers the bonding wire 940 and the active surface 920a of the chip 920, the volume occupied by the molding compound 930 is greatly reduced. The package structure similar to the package structure 900 of FIG. 1 is a window ball grid array (WBGA) package structure, which has been increasingly widely used in various products, and recently, the main application is to be used on the package structure of a memory.
However, the molding compound 930 is a fluid. In the packaging process, after the molding compound 930 covers the bonding wire 940 and the active surface 920a of the chip 920, the molding compound 930 is cured upon being heated. Therefore, during the manufacturing process, the molding compound 930 may flow towards the solder-ball mounting pad 912 along a surface of the package substrate 910, such that the structural strength of the adhesion between the solder ball 950 and the solder-ball mounting pad 912 is seriously affected, and the product yield is greatly reduced.
Besides the problem that the molding compound contaminates the solder-ball mounting pad, in the WBGA package structure of FIG. 1, the package structure with the molding compound and any pad located on the same surface as the package substrate has the similar problem. Therefore, it is one of the important directions for the current research and development of how to solve the above problem.